Overexpression of the P46 (T1) translocase component of the glucose-6-phosphatase complex in hepatocytes impairs glycogen accumulation via hydrolysis of glucose 1-phosphate.

Published

Journal Article

The final step of gluconeogenesis and glycogenolysis is catalyzed by the glucose-6-phosphatase (Glc-6-Pase) enzyme complex, located in the endoplasmic reticulum. The complex consists of a 36-kDa catalytic subunit (P36), a 46-kDa glucose 6-phosphate translocase (P46), and putative glucose and inorganic phosphate transporters. Mutations in the genes encoding P36 or P46 have been linked to glycogen storage diseases type Ia and type Ib, respectively. However, the relative roles of these two proteins in control of the rate of glucose 6-phosphate hydrolysis have not been defined. To gain insight into this area, we have constructed a recombinant adenovirus containing the cDNA encoding human P46 (AdCMV-P46) and treated rat hepatocytes with this virus, or a virus encoding P36 (AdCMV-P36), or the combination of both viruses, resulting in large and equivalent increases in expression of the transgenes within 8-24 h of viral treatment. The overexpressed P46 protein was appropriately targeted to hepatocyte microsomes and caused a 58% increase in glucose 6-phosphate hydrolysis in nondetergent-treated (intact) microsomal preparations relative to controls, whereas overexpression of P36 caused a 3.6-fold increase. Overexpression of P46 caused a 50% inhibition of glycogen accumulation in hepatocytes from fasted rats incubated at 25 mm glucose relative to cells treated with a control virus (AdCMV-betaGAL). Furthermore, in hepatocytes from fed rats cultured at 25 mm glucose and then exposed to 15 mm glucose, AdCMV-P46 treatment activated glycogenolysis, as indicated by a 50% reduction in glycogen content relative to AdCMV-betaGAL-treated controls. In contrast, overexpression of P46 had only small effects on glycolysis, whereas overexpression of P36 had large effects on both glycogen metabolism and glycolysis, even in the presence of co-overexpressed glucokinase. Finally, P46 overexpression enhanced glucose 1-phosphate but not fructose 6-phosphate hydrolysis in intact microsomes, providing a mechanism by which P46 overexpression may exert its preferential effects on glycogen metabolism.

Full Text

Duke Authors

Cited Authors

  • An, J; Li, Y; van De Werve, G; Newgard, CB

Published Date

  • April 6, 2001

Published In

Volume / Issue

  • 276 / 14

Start / End Page

  • 10722 - 10729

PubMed ID

  • 11148207

Pubmed Central ID

  • 11148207

International Standard Serial Number (ISSN)

  • 0021-9258

Digital Object Identifier (DOI)

  • 10.1074/jbc.M009525200

Language

  • eng

Conference Location

  • United States